I downloaded satellite images but mtl files were not in the zip. I searched a lot but i dint get from where to download mtl files. I need to convert radiance to temperature in both L7 and L8 images.
The USGS provides a tool for bulk downloading of Landsat Metadata: Landsat Bulk Metadata Service
The MTL files will allways be distributed with the data if you download the scenes through USGS EarthExplorer.
If you don't want to download the bands again and just the MTL text files for each scene you can take a look at Amazons Landsat Mirror. Each scene is in a subfolder also containing a MTL text file with the metadata.